The Central Board of Secondary Education (CBSE) will hold the Class 12 Physics examination on February 20, 2026 . This exam is part of the larger CBSE Class 12 board examinations, which will take place from February 17 to April 10, 2026 . Students preparing for the Physics paper should pay close attention to derivations, as they are crucial for scoring high marks in the upcoming exam.
The Physics exam will be for a total of 70 marks , and students will get 3 hours to complete it. The question paper will include different types of questions: 50% will be competency-based questions (such as multiple-choice questions, case studies, or questions based on provided sources), 20% will be standard multiple-choice questions, and 30% will be descriptive questions where students write out their answers. Derivations often appear in this descriptive part of the exam, carrying significant marks, typically 3-mark and 5-mark questions.
Key Derivations for CBSE Class 12 Physics 2026
To help students prepare thoroughly for the upcoming examination, here is a list of important derivations. These are frequently asked questions in the exam, and mastering them can significantly boost your scores. We have grouped them by chapter for easier study:
- Chapter 1: Electric Charges & Fields
This chapter deals with the fundamental concepts of electric charge and fields. Important derivations include:
- Electric Field calculation due to a uniformly Charged Plate using Gauss's Law.
- Derivation of the Torque experienced by an Electric Dipole when placed in a uniform Electric Field.
- Electric Field determination due to a Spherical Shell, applying Gauss's Law.
- Finding the Electric Field due to an Infinitely Long Thin Wire, also through Gauss's Law.
- Chapter 2: Electrostatic Potential & Capacitance
Focus on how electric potential works and how capacitors store energy. Key derivations are:
- Derivation for the Capacitance of a Parallel Plate Capacitor when a dielectric material partially fills the space between the plates.
- Expression for the Energy stored in an Electric Dipole when it is placed in a uniform Electric Field.
- Derivation for the Capacitance of a basic Parallel Plate Capacitor.
- Chapter 3: Current Electricity
Understand the flow of charge and how circuits work. Essential derivations cover:
- The relationship between electric Current and the Drift Velocity of electrons.
- Derivation for the Equivalent Electromotive Force (EMF) when multiple cells are joined in a Parallel combination.
- Chapter 4: Moving Charges & Magnetism
This chapter explores the magnetic effects of electric current. Important derivations include:
- The force acting between two Current Carrying Parallel Wires.
- Magnetic Field calculation at the Centre of a Current Carrying Circular Coil.
- Determining the Magnetic Field along the axis of a Current Carrying Circular Loop.
- Chapter 6: Electromagnetic Induction
Learn about how changing magnetic fields can produce electric current. A key derivation here is:
- Derivation for the Mutual Inductance of two Solenoids.
- Chapter 9: Ray Optics and Optical Instruments
This section covers light's behavior and optical devices. Must-do derivations are:
- Formula for Refraction at Spherical Surfaces.
- Derivation of the Magnifying Power of a Compound Microscope when the final image is formed at the least distance of distinct vision (D).
- Magnifying Power of a Telescope when the final image is formed at Infinity.
- The relation between Refractive Index and the minimum deviation angle for a Prism.
- Derivation of the Lens Maker's Formula.
- Chapter 10: Wave Optics
Understand light as a wave and its properties. A crucial derivation from this chapter is:
- Deriving Snell's Law through Huygens' Wave Theory.
How to Prepare Derivations Effectively
Students should follow these tips to do well in derivation questions and avoid losing marks:
- Draw Diagrams: Always start each derivation with a clear, neat, and correctly labeled diagram. Marks are often deducted if the diagram is missing.
- State Assumptions: Clearly mention any assumptions made before starting the mathematical steps. For example, in optics, you might need to assume a "small aperture" or "thin lens".
- Box Final Formulas: Once you reach the final formula, draw a box around it to make it stand out.
- Include Units: Always write the correct units for physical quantities in the final formula, where applicable.
Practicing these derivations carefully will help Class 12 students feel more confident and score higher in the upcoming CBSE Physics exam for 2026. Good luck with your preparation!
